Aircraft: EMB ERJ 145 ER/LR
Phase of flight: Cruise
Anomaly: ATC Issue All Types; Inflight Event / Encounter Fuel Issue; Inflight Event / Encounter Weather / Turbulence

We were given a series of re-routes along with radar vectors. In addition to the ATC re-routes; we the flight crew also needed to deviate to avoid thunderstorms and make our way through a line of weather en-route to ZZZ. The last few ATC re-routes put us in a situation that would have resulted in landing at our alternate with approximately 300 lbs of fuel. This would have been an unacceptable situation; and a risk I was not willing to accept. As a result I [advised] Min fuel. Neither [advising] helped our situation as ATC was still issuing us re-routes for arrivals further west of ZZZ; for which we did not have the fuel for. I then [advised ATC] a fuel emergency and told ZZZ center that we would not be flying the arrival and at that point I needed to go direct to ZZZZZ intersection on the arrival and would be doing so within a 2 min time frame. The ATC gave us direct ZZZ VOR; Direct ZZZ1 VOR; Direct ZZZ Airport. This new clearance provided us the fuel to continue to ZZZ safely and then go to our alternate with plenty of fuel. The weather at this point in ZZZ was heavy rain with thunderstorms. Due to now having a favorable plan to land with plenty of fuel we continued to ZZZ and landed with no further issue. The threat was that we would not have enough fuel to continue to our alternate of ZZZ1 if we had not changed the flight plan. Due to ATC not allowing us to continue on our planned route and further issuances of re-routes making the situation progressively worse; we (the flight crew) were forced to exercise our emergency authority to fix the fuel situation. Another threat was what seemed to be our Dispatcher's inability to keep up with the pace of ACARS messages we sent to her. At one point she also sent us a message saying we could drop our alternate; and at the same point we were getting ATIS updates at the field that indicated gusty winds with Thunderstorms and Heavy Rain. Dropping the alternate was NOT something I was willing to Risk. I think I should have [advised] min-fuel sooner; however it is tough to determine how much sooner as the pace of the re-routes prior to [advising ATC] was fairly quick. Other than that I felt our decision to [advise ATC]; sealed the deal to have plenty of fuel to continue to ZZZ and then land at our alternate with plenty of fuel was a good one. With the significant amount of storms around ZZZ that night we needed to have the extra fuel just in case something happened and the only way we felt at the time to do that was to not fly the full arrival which would have used too much of our alternate fuel. Also I think it is worth mentioning that as soon as we realized the dispatcher could not keep up with the flight we relied heavily on our experience and the Performance data on the FMS to determine that we needed to take the measures of declaring Min fuel. [Report narrative contained no additional information]. EMB-145 flight crew reports receiving reroutes and vectors along their route for weather; leading to a declaration of minimum fuel with ATC. With no perceived change in the way they are being handled by ATC. They advised ATC of a low fuel urgency situation. This achieves the desired results and the flight lands safely.